DE4108915A1 - Hydraulic medium supply device for servo steering - has variable displacement pump for normal supply, and smaller volume constant pump - Google Patents

Abstract

The device is for supply of pressure medium to a priority primary load circuit, and at least one auxiliary load circuit, e.g. servo steering in a motor vehicle. It has a first and a second fluid source, and associated priority valves. The first fluid source is formed by a variable displacement pump (16), which has a larger volume the constant pump (17), forming the second source. The control pressure connection (19) of this is charged by a second load pressure signal (43), and additionally by a first signal (36, 42) from the primary circuit (11). The second pirority valves (45) are regulated dependant upon the differential load pressure signal, which regulates the flow volume requirements in the primary circuit. The active pressure differential (32), to control the fist priority valves (23), is larger than the pressure differential (55) to control the second priority valves. USE - Hydraulic power supply for vehicle servo steering.

Description

State of the art

The invention relates to a hydraulic device Pressure medium supply to a privileged primary load circuit and at least one auxiliary load circuit according to that in the preamble of An say 1 specified genus.

Such a hydraulic device for supplying pressure medium is already known from DE 27 33 054 A1, in particular FIG. 4, in which a first constant pump and a second variable pump each supply a primary load circuit designed as a steering system with fluid via a priority valve, the Excess pressure medium flows of both fluid sources can be controlled to auxiliary load circuits. In this device, both priority valves are connected in parallel and can be impacted by a load pressure difference signal from the primary load circuit, but the load pressure signal to the second priority valve is controlled via an additional switching valve as a function of the output pressure at an auxiliary output of the first priority valve. With this device it can be disadvantageous in some cases that the second priority valve is not controlled directly by the load pressure difference signal in the primary load circuit, the size of which represents a measure of the fluid requirement in the steering circuit, but is only influenced by a signal derived therefrom. This control not only leads to increased effort, but also to increased energy losses, since the auxiliary outlet of the first priority valve is always relieved to the tank via a throttle point. A disadvantage of this device is also that the second fluid source, which is designed as a variable displacement pump in LS technology, can not come under pressure if the connected LS directional control valves in the auxiliary load circuit are not actuated and thus a load pressure signal is missing. The known device essentially assumes that two pumps of the same size are used as fluid sources. In some cases, this can be unfavorable for the use of energy, especially if a constant flow pump is used as the fluid source for the primary load circuit designed as a steering circuit. In many cases it can be disadvantageous that two pumps of essentially the same size lead to a relatively expensive device. Especially in heavy vehicles with hydrostatic power steering, if the main pressure supply fails, the steering forces are greater than those permitted by law. A second independent pressure supply is therefore necessary, which is switched on automatically for the primary load circuit in the event of an emergency, i.e. if the main pressure supply fails. Especially for such an emergency steering device, the known hydraulic device is less suitable.

Advantages of the invention

The hydraulic device according to the invention for pressure medium supply a privileged primary load group and at least one Auxiliary load circuit with the characteristic features of the main On the other hand, saying has the advantage that Cost of pump capacity and control means inexpensive and relatively simple design allows an energy-saving and safe re pressure medium supply of several load circuits with different  Priority enabled. The facility is particularly suitable as an emergency steering device for hydrostatic power steering in heavy Vehicles where an automatic failure of the main pressure supply Emergency pressure supply is switched on. While for normal printing supply of privileged hydrostatic steering in LS technology and an additional auxiliary load circuit with LS-Wegeven tilen a load pressure controlled variable displacement pump with a correspondingly large Funding volume takes place, the con Pump with a smaller delivery volume either circulate empty or supply another auxiliary load circuit with pressure medium. Only in In an emergency, the constant pump supplies the primary load circuit and provides also a possibly excess residual current for additional radio available. The relatively large, load-controlled variable pump combined with a small constant pump enables a cost inexpensive and space-saving design.

The measures listed in the subclaims provide for partial further developments and improvements in claim 1 given hydraulic device possible. One is advantageous Design according to claim 2, whereby a relatively simple Lö solution with commercially available priority valves and a switching valve can be realized. Training after is particularly useful Claim 3, whereby the device with two commercially available Priority valves and can be realized without a switching valve, so that achieved a particularly inexpensive and space-saving design becomes. Furthermore, it is expedient if the device according to claim 6 is formed because the constant pump is particularly suitable for pressure supply of an additional brake circuit is suitable. A special one compact and cost-effective set-up is possible with execution stungen according to claims 7 to 9, if both priority valve with tel are united in a single valve. More advantageous off designs result from the other claims, the description exercise as well as the drawing.  

drawing

Three embodiments of the invention are shown in the drawing represents and explained in more detail in the following description. It demonstrate

Fig. 1 shows a first embodiment of the hydraulic device for supplying pressure medium to a privileged primary load circuit and at least one auxiliary load circuit in a simplified representation and FIGS . 2 and 3, a second and third embodiment of the device approximately.

Description of the embodiments

Fig. 1 shows a first hydraulic device 10 for supplying pressure medium to a privileged primary load circuit, which is designed here as a hydrostatic power steering device 11 and a subordinate supplied auxiliary load circuit 12 , which is known per se and not shown from directional valves for load pressure-compensated control. Furthermore, the Einrich device 10 includes a second auxiliary load circuit 13 , which consists of a switched in a circulation channel 14 to the brake valve 15 . The device 10 comprises a pressure pump 16 as a first fluid source and a constant pump 17 as a second fluid source, which are mechanically driven together by a motor 18 . The United pump 16 is designed with its delivery volume so large that it can serve as the main pressure supply for the power steering device 11 and for the first auxiliary load circuit 12 . It therefore has a significantly larger delivery volume than the constant pump 17 , it being favorable if the ratio is greater than 2: 1. The United pump 16 is designed as a load pressure-controlled pump, for which purpose it can be beaten to a control pressure connection 19 with a load pressure signal.

The variable displacement pump 16 draws in pressure medium from a tank 21 and delivers it to an inlet 22 of a first priority valve 23 . The first priority valve 23 has a main outlet 24 which is connected via a line 25 with a check valve 26 opening towards the load with an inlet connection 27 of the power steering device 11 . A second line 29 leads from an auxiliary outlet 28 of the priority valve 23 to the auxiliary load circuit 12 . The first priority valve 23 is a known, commercially available valve, the control slide 31 of which is loaded by a spring 32 in the direction of an initial position 33 , in which the entire fluid flow of the variable displacement pump 16 is preferred to the preferred primary load circuit 11 is controlled. The control slide 31 of the first priority valve 23 is acted upon in the direction of the prestress of the spring 32 by a pressure in a first control connection 34, which is supplied via a first control line 35 with a load pressure signal from a signal output 36 of the power steering device 11 . Furthermore, the control slide 31 is acted upon by the pressure in the main outlet 24 against a force of the spring 32 via a second control connection 37 . The control slide 31 of the first priority valve 23 is thus acted against the force of the spring 32 by a Lastdruckdif reference signal, which is tapped via the connections 27 , 36 of the power steering device 11 , and the size of which is a measure of whether the primary load circuit 11 with a sufficient Volume flow is supplied. If the load pressure difference signal from the power steering device 11 designed in LS technology exceeds the value specified by the spring 32 , the priority valve 23 throttles the volume flow flowing from the variable displacement pump 16 to the primary load circuit 11 , while at the same time the excess pressure medium flow to the auxiliary load circuit 12 is controlled. The entire volume flow of the variable displacement pump 16 to the first auxiliary load circuit 12 is controlled in an outer switching position 38 of the priority valve 23 . The output side of the variable displacement pump 16 is protected by a first pressure relief valve 39 .

The primary load circuit 11 and the auxiliary load circuit 12 work with the variable displacement pump 16 in LS technology, for which purpose the control pressure connection 19 to the variable displacement pump 16 via a first shuttle valve 41 via a second control line 42 with a first load pressure signal from the signal connection 36 of the primary load circuit 11 or a third control line 43 can be supplied with a second load pressure signal from the auxiliary load circuit 12 .

Serving as a second fluid source constant pump 17 is laid out for a ge compared to the variable displacement pump 16 significantly smaller delivery volume and promotes the pressure medium drawn from the tank 21 to an inlet 44 of a second priority valve 45 , which is constructed identically to the first priority valve 23 . Its main outlet 46 is connected via a second line 47 with a second check valve 48 parallel to the first line 25 to the inlet connection 27 of the primary load circuit 11 . The circulation channel 14 is connected to the auxiliary outlet 49 of the second priority valve 45 as part of a second auxiliary load circuit 13 . The circulation channel 14 establishes an unthrottled connection to the tank 21 . The second priority valve 45 has a control element 51 which is loaded by a spring 52 in the direction of its starting position 33 and can be deflected in a pressure-dependent manner. The second control port 37 of the second priority valve 45 is acted upon in a comparable manner by the pressure in the main outlet 46 . The first control connection 34 on the second priority valve 45 is connected via a fourth control line 53 to the signal connection 36 in the power steering device 11 , in which fourth control line 53 a 3/2-way valve 54 is connected. The first load pressure signal from the power steering device 11 is thus transmitted via the fourth control line 53 to the first port 34 on the second priority valve 45 when the switching valve 54 is held by its spring 55 in the illustrated basic position 56 , in which a connection to the tank is blocked. The switching valve 54 can be deflected from the load pressure difference signal brought up from the primary load circuit 11 via the fourth control line 53 and a fifth control line 57 into a working position 58 in which it interrupts the forwarding of the first load pressure signal via the fourth control line 53 and the first control connection 34 second priority valve 45 relieved to tank 21 . The switching valve 54 is thus as the first priority valve 23 controls from the same load pressure difference signal from the primary load circuit 11 is, however, the switching valve 54 is set response value by means of its spring 55 to an opposite to the first priority valve 23 lower on.

The pressure side of the constant pump 17 is secured by a second pressure relief valve 59 . To the second line 47 between the second priority valve 45 and power steering device 11 , an electrohydraulic pressure sensor 61 is connected, which together with an evaluation electronics 62 forms a signal device 63 , which indicates the failure of the main pressure supply and a jump-in of the emergency steering device by monitoring various pressure levels.

The operation of the device 10 is explained as follows: It is based on the basic consideration that a load pressure-controlled variable displacement pump 16 designed for larger delivery volumes supplies the privileged primary load circuit 11 with pressure medium, excess pressure medium receiving the subordinate consumers in the auxiliary load circuit 12 . If this main pressure supply fails, an emergency steering device is automatically switched on, the constant pump 17 preferentially supplying the power steering device 11 with pressure medium, while at the same time a possibly overflowing fluid flow is available for other functions.

The variable displacement pump 16 is acted upon by the maximum load pressure from the primary load circuit 11 and the auxiliary load circuit 12 and supplies the servo steering device 11 with pressure medium via the first priority valve 23 . The volume flow not required by the power steering device 11 flows via the second line 29 into the auxiliary load circuit 12 and is available there for controlling further consumers. The tapped at the connections 27 , 36 load pressure difference signal of the power steering device 11 is a measure of the size of the volume flow through the primary load circuit 11 and speaks ent essentially the control pressure gradient between the adjusting pump 16 and the signal connection 36th The load pressure difference signal acts on both the first priority valve 23 and the switching valve 54 , and is monitored by the latter ( 54 ). The switching valve 54 is adjusted with the help of its spring 55 to a slightly lower response value than the first priority valve 23 with its spring 32 . Therefore, as long as the variable displacement pump 16 controls a sufficiently large volume flow to the primary load circuit 11 , a pressure value above the response value of the load pressure difference signal is generated, which presses the switching valve 54 into its working position 58 and holds it there. As a result, the first control connection 34 of the second priority valve 45 to the tank 21 is relieved and the control slide 51 in the priority valve 45 is deflected into its outer working position 38 , in which the pressure medium delivered by the constant pump 17 is practically unthrottled via the circulation channel 14 , with the brake valve 15 not actuated , is promoted to tank 21 . The constant pump 16 can thus run empty. If necessary, the brake valve 15 can be operated, the pressure medium supply by the constant pump 17 is sufficient.

If the monitored with the help of the switching valve 54 load pressure difference signal in the primary load circuit 11 below the set value, this is an indication that the variable pump 16 no longer provides enough pressure medium for the operation of the power steering device 11 available. The switching valve 54 is switched by its spring 55 into its basic position 56 , so that the first load pressure signal picked up in the signal connection 36 of the power steering device 11 is switched via the fourth control line 53 to the first control connection 34 of the second priority valve 45 . Thus, the load pressure difference signal at the second priority valve 45 is effective, which now primarily supplies the power steering device 11 with the pressure medium flow conveyed by the constant pump 17 , a possibly overflowing fluid flow being led into the second auxiliary load circuit 13 . Depending on whether the variable displacement pump 16 has failed completely or partly, part streams can both pumps 16 and 17, the Ser volenkeinrichtung 11 supplied with fluid flow or may in total failure of the variable displacement pump 16 and the fixed displacement pump 17 to supply only the primary load circuit 11 with pressurized oil . This allows an emergency steering device to be realized, which is automatically switched on by the variable pump 16 if the main pressure supply fails. The circuit in the device 10 ensures that the second priority valve 45 cooperates with the power steering device 11 in the manner of an LS system even in the event of emergency steering with the constant pump 17 .

With the help of the pressure sensor 61 , the operation of the emergency steering device can be monitored so that the failure of the main pressure supply and the intervention of the emergency steering device are displayed to a driver.

The priority valves 23 and 45 shown in FIG. 1 are interpreted as first priority valve means 23 and second priority valve means 45 .

Fig. 2 shows a second hydraulic device 70 for supplying pressure medium to a privileged primary load circuit and at least an auxiliary load circuit, the second device 70 differing from the first device 10 according to FIG. 1 as follows, the same components being provided with the same reference numerals.

The second device 70 is simplified compared to the first device 10 because a separate switching valve 54 is omitted and the monitoring function is placed directly into the second priority valve 45 . For this purpose, the second priority valve 45 has a weaker spring 71 , so that the second priority valve 45 responds to a lower load pressure difference signal than the first priority valve 23 . The fourth control line 53 from the signal connection 36 of the power steering device 11 therefore leads directly to the first control connection 34 of the second priority valve 45 . The second control port 37 of the second priority valve 45 can be pressurized as before with the pressure in the main outlet 46 via a sixth control line 72 . Furthermore, a second shuttle valve 73 is connected in the sixth control line 72 , so that, alternatively to the pressure in the main outlet 46 of the second priority valve 45, the output pressure of the variable displacement pump 16 can act via the shuttle valve 73 in the second control connection 37 of the second priority valve 45 . Furthermore, a first flow indicator 74 is connected upstream of the second priority valve 45 into the volume flow coming from the constant pump 17 , while a second flow indicator 75 is located in the second line 47 . These flow indicators 74 , 75 also represent signaling devices with which the failure of the main pressure supply and the intervention of the emergency steering device can be indicated to the driver.

The operation of the second device 70 corresponds in terms of the main pressure supply of the primary load circuit 11 and the first auxiliary load circuit 12 with the aid of the variable displacement pump 16 and the function of the automatically activated emergency steering pump 17 fundamentally to that of the first device 10 . Due to the opposite of the spring 32 weaker in the first priority valve 23 formed spring 72 in the second priority valve 45, the monitoring function for the volume flow requirement of the primary load circuit 11 can be directly integrated in the second priority valve 45 so that a further valve element and associated control lines can be saved. With help of the second shuttle valve 73 it is ensured that the respective load pressure difference signal can take effect.

In the second device 70 as well , the two priority valves 23 and 45 can be understood as first ( 23 ) and second priority valve means 45 .

Fig. 3 shows a third device 80 for Druckmittelversor supply of privileged primary load circuit 11 and at least one auxiliary load circuit 12, with the third device 80 differs from the first device 10 of FIG. 1 as follows, wherein the same for the same components reference numerals are used.

While commercially available components can be used in the first control device 10 for the two priority valves and the switching valve, the functions of these three components are combined in the third device 80 in a single priority valve 81 , which must be designed in a special manner. The priority valve 81 is designed as a 5-way control valve, which has a first inlet 82 and a second inlet 83 for connection to the variable displacement pump 16 and the constant pump 17 in a comparable manner. For the connection of the primary load circuit 11 , a single main outlet 84 is sufficient, while the second line 29 to the first auxiliary load circuit 12 is located at a first auxiliary outlet 85 and the circulation channel 14 is connected to a second auxiliary outlet 86 . A spool 87 of the priority valve 81 is loaded by a spring 88 in the direction of an initial position 89 , in which the two te inlet 83 is connected to the main outlet 84 , while the connection to the second auxiliary outlet 86 and thus to the second auxiliary load circuit at least throttled or also is completely cordoned off. Furthermore, the first auxiliary outlet 85 is hydraulically blocked in this starting position 89 . The first inlet 82 is secured by a check valve 91 arranged in the valve housing, but still allows a pressure medium flow from the first inlet 82 to the main outlet 84 . When priority valve 81 , an intermediate position 92 is shown adjacent to the starting position 89 , in which the first inlet 82 is unthrottled connected to the main outlet 84 , while the connec tion from the first inlet 82 to the first auxiliary outlet 85 is throttled. The second inlet 83 is connected to the second auxiliary outlet 86 unthrottled. Finally, an outer switching position 93 that can be reached by the control slide 87 at maximum deflection is shown, in which the main outlet 84 is hydraulically blocked and the first inlet 82 has an unthrottled connection to the first auxiliary outlet 85 , while the second inlet 83 has an unthrottled connection to the second auxiliary outlet 86 communicates. Of course, these switching positions 89 , 92 , 93 only show a greatly simplified representation of the priority valve 81 , the control slide 87 of which has a number of additional intermediate positions for a suitable control for the required control function. The control slide 87 is acted upon in a comparable manner by the load pressure difference signal of the servo steering device 11 against the force of the spring 88 , for which purpose the priority valve 81 has first and second control connections 94 and 95 in a corresponding manner. In the priority valve 81 , the control connections in the more external switch positions 91 and 93 represent first priority valve means 96 , which take over the control functions of the first priority valve 23 according to FIG. 1 in a corresponding manner. In contrast, the inner positions in the form of the starting position 89 and the intermediate position 92 form second priority valve means 97 , which take over the function of the second priority valve 45 in FIG. 1 in a corresponding manner. When working the first priority valve means 96 , the spring 88 must be compressed more than when working the second priority valve means 97 , so that in this way the function of the switching valve 54 according to FIG. 1 to take effect of the second priority valve means 97 at a lower load pressure difference signal in the priority valve 81 is integrated with.

The mode of operation of the third device 80 is explained as follows, the basic function of the first device 10 according to FIG. 1 being assumed to be known in this context. As long as a sufficiently large load pressure difference signal is generated when the variable displacement pump 16 is in the servo steering device 11 , the first priority valve means 96 are effective in the priority valve 81 , the fluid flow from the variable pump 16 via the priority valve 81 primarily to the primary load circuit 11 and primarily to the first auxiliary load circuit 12 is distributed. During the water function, the volume flow of the rotating constant pump 17 can be promoted unthrottled via the priority valve 81 into the circulation channel 14 and thus to the second auxiliary load circuit 13 . Now drops the load pressure difference signal in the power steering device 11 below the pressure drop predetermined by the spring 88 in the priority valve 81 , the control slide 87 is deflected further to the right, so that instead of the first ( 96 ), the second priority valve means 97 are effective sam. This means that, in the event of an emergency steering, the fluid flow from the constant pump 4 via the priority valve 81 is primarily supplied to the power steering device 11 , while a possibly excess pressure medium flow from the constant pump 17 is guided via the second auxiliary circuit 13 .

With the help of a switch 99 , the position of the control slide 87 can be scanned and a statement can be made for the driver as to whether the main pressure supply has been suspended and the emergency steering device is automatically switched on. By integrating the function of three valves according to FIG. 1 in a single priority valve 81 , a particularly inexpensive and compact design is achieved, which is particularly suitable for mobile applications.

Of course, changes are possible in the embodiments shown without departing from the spirit of the invention. Although particularly suitable for the second auxiliary load circuit 13, the brake valve 15, the fixed displacement pump can be dervolumens operated 17 due to its relatively small För without additional load in the circulation duct 14 or it can be other load circuits such as circuit or, for example, a filter, a cooling circuit to be operated. Especially before is geous if the rotating constant pump 17 is used as a pre-feed pump for the variable displacement pump 16 . In addition, it is possible, in the second device 70 according to FIG. 2, to move the pressure tap for the second shuttle valve 73 from the point upstream from the first priority valve 23 downstream, so that it is tapped from the first line 25 . Also, the shuttle valve 73 could be omitted entirely, and instead the control line from the second control port 37 of the second priority valve 45 leads directly to the inlet port 27 of the power steering device 11 . It when the delivery volume of the variable displacement pump 16 carries at least double the constant pump 17 be particularly favorable.

Claims (13)

1. Hydraulic device for supplying pressure medium to a legitimate primary load circuit and at least one auxiliary load circuit, with a first fluid source and associated first priority valves, which feed fluid coming from the first fluid source via a main outlet primarily to the primary load circuit and via an auxiliary outlet to the auxiliary load circuit, and with a second fluid source and associated second priority valve means, the fluid via a main outlet primarily and in addition to the fluid flow via the first priority valve means to the primary load circuit and the residual flow via an auxiliary outlet subordinate to an auxiliary circuit, the primary load circuit providing a device for dispensing a fluid for the Primary load circuit characterizing load pressure difference signal and the change of this load pressure difference signal the distribution of the fluid flows through the two priority valve means to the primary, auxiliary slast or auxiliary circuits influences, and in which device the fluid sources have a load pressure controlled variable displacement pump and a constant pump, of which the variable pump processes a second load pressure signal applied to a control pressure connection from an auxiliary load circuit which has control elements designed in LS technology, characterized in that the first fluid source is the variable displacement pump ( 16 ), the delivery volume of which is larger than that of the constant pump ( 17 ), that its control pressure connection ( 19 ) in addition to the second load pressure signal ( 43 ) also from the first load pressure signal ( 36 , 42 ) from the Primary load circuit ( 11 ) can be acted on so that the second priority valve means ( 45 ; 97 ) depending on the load pressure difference which is decisive for the volume flow requirement in the primary load circuit ( 11 ) and that the effective pressure difference ( 32 ; 88 ) for controlling the first priority valve means ( 23 ; 96 ) versus the pressure difference ( 55 ; 71 ; 88 ) Control of the second priority valve means ( 45 ; 97 ) is larger. 2. Hydraulic device according to claim 1, characterized in that the first and second priority valve means are designed as mutually identical priority valves ( 23 , 45 ), each biased by a spring ( 32 ; 52 ) in the direction of an initial position ( 33 ) are in which essentially the entire fluid flow of the respective fluid source ( 16 , 17 ) to the primary load circuit ( 11 ) is controlled and that a switching valve ( 54 ) acted upon by the load pressure difference signal is provided, which is the second priority valve ( 45 ) via a control line ge (53) led load pressure signal (36) of the primary load pressure circuit (11) by comparing it transmits this signal when a is exceeded (54) of predetermined value at the switching valve in the primary load circuit (11) and fer ner a pressure relief on the second priority valve (45) Doomed gently if this predetermined value is exceeded, the on the switching valve ( 54 ) for the load pressure difference signal in the primary load circuit ( 11 ) predetermined value ( 55 ) is lower than the value on the first priority valve ( 23 ) ( 32 ) ( Fig. 1). 3. Hydraulic device according to claim 1, characterized in that the first and second priority valve means are each formed as mutually identical priority valves ( 23 , 45 ), each of a spring ( 32 , 71 ) towards egg ner starting position ( 33 ) are biased, in which the entire fluid flow of the connected fluid sources ( 16 , 17 ) to the primary load circuit ( 11 ) is essentially controlled that the spring ( 71 ) on the second priority valve ( 45 ) is opposite to the spring ( 32 ) at the first priority valve ( 23 ) is a lower pressure value and that both priority valves ( 23 , 45 ) can be controlled directly by the load pressure difference signal of the primary load circuit ( 11 ) ( Fig. 2). 4. Hydraulic device according to claim 3, wherein the two main outlets ( 24 , 46 ) of the two priority valves ( 23 , 45 ) are each connected via a check valve ( 26 , 48 ) in parallel to the inlet connection ( 27 ) of the primary load circuit ( 11 ), thereby characterized in that at the second priority valve ( 45 ) the spring ( 71 ) counteracting control pressure side ( 37 ) via a shuttle valve ( 73 ) from the pressures in both fluid flows via the main outlets ( 24 , 46 ) upstream of the check valves ( 26 , 48 ) is. 5. Hydraulic device according to claim 4, characterized in that the shuttle valve ( 73 ) is connected to one of its two inputs to the output of the variable displacement pump ( 16 ). 6. Hydraulic device according to one of claims 1 to 5, characterized in that the auxiliary outlet ( 49 ) of the second priority valve ( 45 ) via a circulation channel ( 14 ) to a tank ( 21 ) ent is loaded and that in particular in this circulation channel ( 14 ) a brake valve ( 15 ) is switched. 7. Hydraulic device according to claim 1, characterized in that the first ( 96 ) and the second priority valve means ( 97 ) are formed in a single priority valve ( 81 ), the one to the variable displacement pump ( 16 ) connected to the first main inlet ( 82 ), egg NEN connected to the constant pump ( 17 ) second main inlet ( 83 ), a main outlet ( 84 ) for the primary load circuit ( 11 ), a first auxiliary outlet ( 85 ) for the auxiliary load circuit ( 12 ) in LS technology and a second auxiliary outlet ( 86 ) for has a circulation channel ( 14 ) ( Fig. 3). 8. Hydraulic device according to claim 7, characterized in that the priority valve ( 81 ) has a by a spring ( 88 ) in the direction of the starting position ( 89 ) biased control slide ( 87 ), and that the control slide ( 87 ) subsequent to this starting position at Actuation in the area with a relatively low pressure difference which has the control connections ( 89 , 92 ) assigned to the second priority valve means ( 97 ) and then in the area with a relatively greater pressure difference which has the control connections ( 92 , 93 ) assigned to the first priority valve means ( 96 ). 9. Hydraulic device according to claim 7 or 8, characterized in that the priority valve ( 81 ) has at least one at maxima ler bias of the spring ( 88 ), outer switching position ( 93 ), in which essentially all the fluid pump ( 16 ) is led to the auxiliary load circuit ( 12 ), the main outlet ( 84 ) is at least throttled or blocked and the second auxiliary outlet ( 86 ) is connected unthrottled to the second main inlet ( 83 ) in such a way that it has at least one intermediate position ( 92 ), in wel cher from the fluid flow of the variable displacement pump ( 16 ) a larger partial flow to the main outlet ( 84 ) and the excess, smaller residual flow are throttled to the first auxiliary outlet ( 85 ), while the second main inlet ( 83 ) is throttled with the second auxiliary outlet ( 86 ) Has connection and that at least one at minimum preload voltage of the spring ( 88 ) assumed initial position ( 89 ) is provided, in which the e rste auxiliary outlet ( 85 ) is blocked, and substantially the full fluid flow of the constant pump ( 17 ) to the main outlet ( 84 ) is guided. 10. Hydraulic device according to claim 9, characterized in that in the starting position ( 89 ) the connection to the second auxiliary outlet ( 86 ) is throttled and the main outlet ( 84 ) connected to the first main inlet ( 82 ) by a towards the primary load circuit ( 11 ) opening check valve ( 91 ) is secured. 11. Hydraulic device according to one of claims 1 to 10, characterized in that the delivery volume of the variable displacement pump ( 16 ) is at least twice as large as that of the constant pump ( 17 ). 12. Hydraulic device according to one of claims 1 to 11, characterized in that the primary load circuit is a hydrostatic power steering device ( 11 ). 13. Hydraulic device according to one or more of claims 1 to 12, characterized in that the working of the constant pump ( 17 ) with failed main pressure supply indicating Signalein devices ( 63 ; 74 , 75 ; 99 ) are provided.